The present invention relates to a fuel vaporization promoting device of an internal combustion engine.
Since the temperature of an engine is normally low when the engine is started, the vaporization of the fuel fed from the carburetor is not fully promoted. As a result, a large amount of the fuel is fed into the cylinder of the engine in the form of liquid fuel, so a good combustion cannot be obtained. Therefore, the amount of harmful components in the exhaust gas is increased, and it is difficult to ensure stable operation of the engine.
In order to promote the vaporization of the fuel when an engine is started, a known fuel vaporization promoting device heats the riser portion of the intake manifold by exhaust gas which is introduced to the riser portion from the exhaust system of the engine. However, using the heat of the exhaust gas for promoting the vaporization of the fuel, has disadvantages in that the thermal efficiency is low and the temperature of the exhaust gas is not instantaneously increased after the engine is started.
To eliminate the above disadvantages, fuel vaporization promoting devices of two different types, which use a Positive Temperature Coefficient Thermistor (hereinafter referred to as a PTC element), have been proposed. The first type has a heater vessel containing the PTC element therein arranged in the riser portion of the intake manifold so that the entire surface of the bottom wall of the heater vessel is in contact with the bottom wall of the intake manifold. The second type has a heater vessel containing the PTC element therein which is inserted into a hole formed in the riser portion of the intake manifold so that the upper face of the heater vessel is exposed to the inside of the intake manifold and the lower face of the heater vessel is exposed to the atmosphere. In either type of device, since the temperature of the PTC element is instantaneously increased when voltage is applied to the PTC element, it is possible to promote the vaporization of the fuel fed from the carburetor immediately after the engine is started.
However, in the case wherein the entire surface of the bottom wall of the heater vessel is in contact with the bottom wall of the intake manifold as in a device of the above-mentioned first type, a large amount of the heat issued from the heater vessel escapes into the atmosphere through the intake manifold, with the disadvantage that the thermal efficiency is low. This is also true in the case wherein the lower face of the heater vessel is exposed to the atmosphere as in a device of the above-mentioned second type, since a large amount of the heat issued from the heater vessel directly escapes into the atmosphere.